1. Technical Field
The disclosure relates to an endoscope system.
2. Related Art
Conventionally, in the medical field, an endoscope system has been used when observing an organ of a subject such as a patient. The endoscope system includes an endoscope and a processing device, for example. The endoscope includes an insertion portion. The insertion portion has an image sensor at a distal end thereof, has a flexible elongated shape, and is configured to be inserted into a subject. The processing device is connected to a proximal end of the insertion portion through a cable, performs image processing on an in-vivo image according to an imaging signal generated by the image sensor, and causes a display unit to display the in-vivo image.
As an observation method used for the endoscope system, there are a simultaneous lighting and a sequential lighting. In the simultaneous lighting, for example, a color filter that transmits light of three color components of red, green, and blue is provided in front of a light receiving unit of the image sensor and imaging is performed under illuminating light of white light. On the other hand, in the sequential lighting, for example, illuminating light of each of three color components of red, green, and blue is sequentially switched. In the sequential lighting, imaging is performed for each color under illuminating light whose color component is sequentially switched. The sequential lighting has an advantage to be able to reduce the diameter of the insertion portion while maintaining a high image quality as compared with the simultaneous lighting.
As the image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor is used. The CMOS image sensor generates an imaging signal by a rolling shutter method that performs reading by shifting timing for each horizontal line. In the CMOS image sensor, it is possible to arbitrarily set how to read pixel information based on a charge accumulated in a pixel, so that it is possible to perform imaging more variously than a CCD image sensor that reads all the pixels at the same time.
In an endoscope system using a CMOS image sensor, when switching a plurality of types of illumination described above according to a frame rate of an image to be captured, an exposure period may overlap with illumination periods different from each other. In this case, there is a problem that an image in which illuminating rays of light of two different illumination periods are mixed is obtained. As a technique to solve the problem, a technique is disclosed which emits illuminating light of the same color component in a period for at least two frames and excludes an imaging signal of a first frame of imaging signals of a plurality of frames, which are exposed by the illuminating light and read out, from a processing target (for example, see JP 5427316 B1). According to JP 5427316 B1, even when a CMOS image sensor is used, under a condition in which a plurality of illuminating rays of light are switched, it is possible to capture an image corresponding to each illuminating light while securing sufficient sensitivity.